who to pay first

[Player101]

how do casinos know who to pay first

[administrator]

On Roulette, The casinos have an 'Order of payout' this is usually starting with the bets on the lowest odds and finishing with the bets on the highest odds. If you have multiple bets, at different odds, connected to the winning number. As soon as your lowest odd chips are in order to be paid, You will receive the total payout for all of your winning bets.
Card games are usually paid from the dealers right to left, this is to allow a clear view of the dealers actions and guard against players tampering with their bet, whilst waiting for their win or loss.